The following function will insert a building block from a named template at a bookmarked location. That bookmark can be in a footer. See also thew example at
https://www.gmayor.com/word_vba_examples_3.htm
Code:
Sub AutoTextToBM(strbmName As String, oTemplate As Template, strAutotext As String)
'strBMName is the name of the bookmark to fill
'oTemplate is the template with the autotext - probably ActiveDocument.AttachedTemplate
'strAutotext is the name of the autotext entry
Dim oRng As Range
On Error GoTo lbl_Exit
With ActiveDocument
Set oRng = .Bookmarks(strbmName).Range
Set oRng = oTemplate.AutoTextEntries(strAutotext).Insert _
(Where:=oRng, RichText:=True)
.Bookmarks.Add Name:=strbmName, Range:=oRng
End With
lbl_Exit:
Exit Sub
End Sub